CDK4/6 inhibition suppresses p73 phosphorylation and activates DR5 to potentiate chemotherapy and immune checkpoint blockade

Targeting cyclin-dependent kinases 4 and 6 (CDK4/6) is a successful therapeutic approach against breast and other solid tumors. Inhibition of CDK4/6 halts cell cycle progression and promotes antitumor immunity. However, the mechanisms underlying the antitumor activity of CDK4/6 inhibitors are not fully understood. We found that CDK4/6 bind and phosphorylate the p53 family member p73 at threonine 86, which sequesters p73 in the cytoplasm. Inhibition of CDK4/6 led to dephosphorylation and nuclear translocation of p73, which transcriptionally activated death receptor 5 (DR5), a cytokine receptor and key component of the extrinsic apoptotic pathway. p73-mediated induction of DR5 by CDK4/6 inhibitors promoted immunogenic cell death (ICD) of cancer cells. Deletion of DR5 in cancer cells in vitro and in vivo abrogated the potentiating effects of CDK4/6 inhibitors on immune cytokine TNF-related apoptosis-inducing ligand (TRAIL), 5-fluorouracil (5-FU) chemotherapy, and anti-PD-1 immunotherapy. Together, these results reveal a previously unrecognized consequence of CDK4/6 inhibition, which may be critical for potentiating the killing and immunogenic effects on cancer cells. mRNA profiles of HCT116 cells, HCT116 cells treated with palbociclib for 24 hours, HCT116 cells transfected with siRNA against CDK4 for 24 hours.

靶向细胞周期蛋白依赖性激酶4和6（CDK4/6）是治疗乳腺癌及其他实体瘤的成熟治疗策略。CDK4/6抑制可阻断细胞周期进程并促进抗肿瘤免疫，但目前CDK4/6抑制剂的抗肿瘤活性背后的分子机制尚未完全阐明。本研究发现，CDK4/6可结合并磷酸化p53家族成员p73的苏氨酸86位点，进而将p73隔离于细胞质中。CDK4/6抑制会导致p73发生去磷酸化并发生核转位，后者可转录激活死亡受体5（DR5）——该受体是一种细胞因子受体，同时也是外源性凋亡通路的关键组分。CDK4/6抑制剂通过p73介导的DR5诱导，可促进癌细胞的免疫原性细胞死亡（ICD）。在体外与体内实验中，癌细胞DR5的敲除会消除CDK4/6抑制剂对免疫细胞因子肿瘤坏死因子相关凋亡诱导配体（TRAIL）、5-氟尿嘧啶（5-FU）化疗以及抗PD-1免疫治疗的增强作用。综上，本研究结果揭示了CDK4/6抑制此前未被报道的生物学效应，该效应可能对增强癌细胞的杀伤效果与免疫原性至关重要。本数据集包含三类样本的mRNA表达谱：未经处理的HCT116细胞、经帕博西尼处理24小时的HCT116细胞，以及转染靶向CDK4的小干扰RNA（siRNA）24小时的HCT116细胞。